<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8"/>
        <meta name="viewport" content="width=device-width, initial-scale=1.0"/>
        <meta http-equiv="X-UA-Compatible" content="ie=edge"/>
        <title>Document</title>
        <style>
            #small{width: 250px; height: 365px; border: 1px solid black; position: absolute; left: 100px; top: 100px}
            #small img{width: 100%; height: 100%;}
            #big img{width: 1000px; height: 1460px; position: absolute}
            #big{ display: none;overflow: hidden;;width: 400px; height: 400px; border: 1px solid black; position: absolute; left: 400px; top: 100px}
            #mask{display: none;width: 100px; height: 100px;background-color: white; opacity: 0.5; filter: alpha(opacity=50); position: absolute; left:0px; top: 0px}
        </style>
        <script src = "jquery-1.10.1.min.js"></script>
        <script>
            /*
				mouseover
				mouseout  这两个事件如果经过子节点，会重复触发

				mouseenter
				mouseleave 这两个事件经过子节点的时候，不会重复触发

			 */
            $(function(){
                $("#small").mouseenter(function(){
                    $("#mask,#big").show()
                }).mouseleave(function(){
                    $("#mask,#big").hide()
                }).mousemove(function(ev){
                    var l = ev.pageX - $(this).offset().left - 50;
                    var t = ev.pageY - $(this).offset().top - 50;
                    if(l <= 0){
                        l = 0;
                    }
                    if(l >= 150){
                        l = 150;
                    }

                    if(t <= 0){
                        t = 0;
                    }
                    if(t >= 265){
                        t = 265;
                    }

                    //改变遮罩层的位置
                    $("#mask").css({
                        left: l,
                        top: t
                    })


                    //同时放大图片的位置，四倍于遮罩层的位置，注意反方向的。
                    $("#big img").css({
                        left: -4 * l, 
                        top: -4 * t
                    })
                })
            })
        </script>
    </head>
    <body>
        <div id = 'small'>
            <img src="1.jpg" alt=""/>
            <div id = 'mask'></div>
        </div>
        <div id = 'big'>
            <img src="1.jpg" alt=""/>
        </div>
    </body>
</html>